The present invention relates to a multi-shaft reheat turbine mechanism for generating power.
There is disclosed in U.S. Pat. Nos. 5,347,806 and 5,386,688 (the disclosures of which being incorporated herein by reference) a multi-shaft reheat turbine mechanism for generating power. One form of that mechanism is depicted schematically in FIG. 4. The power shaft assembly represents a conventional heavy duty combustion turbine or an aircraft derivative combustion turbine which includes a lower pressure compressor 10, an expansion turbine 30, a combustor 20 which feeds heated combustion product gas to the expansion turbine 30, the expansion turbine 30 being coupled to drive the compressor 10, and an electric generator 60A. Two additional shaft assemblies are provided. Also, a heat exchanger in the form of a recuperator 50 is provided which may be a chemical recuperator.
The first additional shaft assembly includes an intercooler 40, an intermediate pressure compressor 110, an intermediate pressure combustor 120 and an intermediate pressure expansion turbine 130. The second additional shaft assembly includes a high pressure intercooler 140, a high pressure compressor 210, a high pressure combustor 220 and a high pressure expansion turbine 230. The intercoolers 40 and 140 are cooled by water supplied from a cooling tower or other water sources (lakes, rivers, etc.)
As shown, the air and gas path extends through the modified compressor of the conventional power shaft assembly, through the intercoolers and compressors of the additional shaft assemblies, through the recuperator, through the combustors and expansion turbines of the additional shaft assemblies, and then through the combustor and expansion turbine of the conventional power shaft assembly. Thus, the exhaust 2 of the lower pressure compressor 10 passes through the intercooler 40 which reduces its temperature at the inlet 11 of the intermediate compressor 110. The pressure of the air is then again raised and provided from the exhaust 12 of the compressor 110 to the intercooler 140 which lowers its temperature and delivers the cooled intermediate pressure air to the inlet 21 of the high pressure compressor 210. The exhaust 22 of the high pressure compressor 210 is provided as an input to the heat recuperator 50. The outlet 5 of the heat recuperator 50 to which fuel has been added, is connected to the high pressure combustor 220, whose outlet 23 is connected to the high pressure expansion turbine 230. The exhaust 24 of the high pressure expansion turbine 230 receives fuel and is heated in the intermediate pressure combustor 120 and then is delivered to the inlet 13 of the intermediate pressure expansion turbine 130. The exhaust 14 of the intermediate pressure expansion turbine 130 receives fuel and is heated in the low pressure combustor 20 and then provided to the inlet 3 of the low pressure expansion turbine 30, the exhaust 4 of which is utilized as a heat source of the heat recuperator 50, before going to the system exhaust 6.
The compression ratio of the compressor 10 is substantially reduced from what it would have been in the absence of the additional shaft assemblies. Accordingly, the turbine 30 can supply more of its power for driving generator 60A. This lowering of the compression pressure ratio of the compressor 10 is accompanied by raising the overall compression pressure ratio of the additional shaft assemblies over the overall expansion pressure ratio of the additional shaft assemblies expansion turbines. By introducing the intercoolers 40 and 140, the temperature of the air entering the compressors 110 and 210 is reduced, which reduces the power consumed by the compressor 110 and 210, and for the same power consumption by the compressors allows for increased compression pressure ratios.
Such a system, also known as a cascaded advanced turbine (CAT) cycle, has achieved improvements in efficiency, compared to a standard recuperated cycle.
Notwithstanding the advantages attained by the above-described system, certain shortcomings exist. For instance, fuel must be added to each of the combustors 220, 120, 20 i.e., at locations that are at high pressure, whereby energy must be expended to elevate the pressure of the incoming fuel. This would be done using a pump for liquid fuels or a compressor for gaseous fuels. Compressors for pre-pressurizing the fuel require substantial energy that reduces the overall efficiency, rendering the system impractical in small capacity generating systems as used, for example, in small commercial or light industrial settings.
Moreover, compressors and pumps represent potential sources of malfunction, thereby diminishing the overall reliability of the system.